Synonyms:

Pachypodium rosulatum var. horombense

Habitat:

Pachypodium horombense originates from the Horombe plateau in southern Madagascar. Its type locality is in Madagascar, specifically on the Ambatolahy-Kelivondraka Road in Fianarantsoa. This species thrives at altitudes ranging from 500 to 1000 meters above sea level. In its natural habitat, Pachypodium horombense is found on granite outcrops situated on hilltops. These hilltops are also home to some of Madagascar’s rarest species, such as Pachypodium brevicaule, Euphorbia quartziticola, Aloe calcairophylla, Aloe isalensis, and Schizolaena tampoketsana.

Description:

Pachypodium horombense is a unique succulent shrublet, standing around 1.5 meters tall, featuring a chubby, bottle-shaped main stem adorned with several short, spiny, fat arms. Each arm carries a rosette of leaves and a single long-peduncled inflorescence, which hosts 3-10 broadly cup-shaped, horizontal, gold flowers during the warm months. The flower has an inflated corolla that creates five large sacs, providing a passage for pollinators. When not flowering, it’s quite challenging to differentiate Pachypodium horombense from the cactus species Pachypodium rosulatum. In terms of its habit, P. horombense presents as a succulent shrub or dwarf tree, reaching up to 60 cm in height. It resembles Pachypodium rosulatum but possesses stiffer and more erect stems that branch closer to the base. The trunk and branches of this plant resemble those of a cactus, adorned with short paired spines. It also possesses a plump tuberous base, known as a caudex, around 50-70 cm in diameter, serving as a swollen trunk-root transitional area for water storage. The trunk measures 20-30 cm in diameter, donning a grey-green, smooth, shiny bark, while the branches measure up to 10 cm in diameter, and branchlets are 20-40 cm long and 6-20 mm in diameter. The branchlets exhibit various twists, bends, and gnarls, all covered with paired straight spines, 3-10 mm long, and 1-3 mm in diameter at the base, with the basal part being conical. Its leaves are thick, stiff, and arranged in a whorled tuft on branch tips. They take an elliptic to narrowly oblong shape, ranging from 25-80 mm in length and 5-20 mm in width, rounded at the apex and wedge-shaped at the base. The leaves boast a deep green, glossy upper surface with a pale green or yellowish midvein and secondary veins. The undersides are white and felted, showcasing paler midribs and dark green reticulate venation. As temperatures cool and the soil dries out during the tropical winter, the leaves are deciduous, dropping away. Pachypodium horombense produces an inflorescence bearing 4-11 chrome-yellow flowers, held on an upright, pubescent peduncle, measuring 10-60 cm in height and 3-8 mm in width. The pedicels are 5-45 mm long and pubescent, while the bracts are pale green, oblong to obovate, 8-25 mm in length and 2-6 mm in width, with an acuminate apex, sometimes concealed by the hairs. The flowers flaunt a bright yellow corolla, with pale green sepals fused at the base for about 0.5 mm. The tube adopts a broadly cup-shaped appearance, approximately 17-23 mm in diameter and 5-lobed in cross-section, showcasing dark red longitudinal lines in bud and pale green in open flowers. The corolla forms a relatively wide ovoid head, measuring 2.5-5.5 cm in length. The basal part appears almost cylindrical, abruptly widening where the stamens are inserted into the upper part, which adopts an urceolate shape, measuring 18-40 mm in length and 15-26 mm in width at the mouth. Inside, there are five widened parts below the lobes, resulting in an interior that is 5-winged. The lobes of the corolla take on an oblique and broadly obovate form. Pachypodium horombense blooms during the warmth and increased moisture of late spring and into summer, with thin flower stalks towering above the leafy branch tips. The fruits are about 14 cm long and 7 mm wide. Moreover, there has been documentation of a wild hybrid between Pachypodium horombense and Pachypodium densiforum.

Cultivation:

Pachypodium horombense is an exceptionally appealing species within its genus, suitable for both indoor and outdoor cultivation in warm climates. It grows moderately and can develop an impressive caudex steadily. In winters, it sheds its leaves, except in very tropical regions. It is quite sensitive to cold and may be prone to rot if exposed to winter wetness. When grown outdoors, it can be showcased as a specimen among rocks and low-growing plants in a hot rockery or in a sturdy container on a sunny patio.For successful cultivation, Pachypodium horombense requires a well-draining, gritty cactus potting mix that isn’t highly acidic. During the growing season, water it sparingly to promote new growth, foliage, and flowering. To avoid waterlogged conditions, use well-drained soil. In late autumn through mid-spring, refrain from watering. Adjust the watering regimen based on temperatures and growth stage, ensuring the plant doesn’t dry out completely for extended periods. For indoor cultivation, keep it on the dry side to prevent rot. During winter, protect it from rain, and avoid leaving it damp in cool weather. As it ages, it will require less water. Regarding hardiness, Pachypodium horombense is sensitive to cold and should be kept completely dry during winter, preferably at around 10°C. However, it shows some cold resilience when dormant, provided the soil remains bone dry. Frost protection is essential. In winter, it tends to lose its leaves and go dormant (USDA Hardiness zones: 10 – 11). This plant thrives in full sun to light shade exposure. Maintenance typically doesn’t require pruning; it naturally takes on an interesting and unusual bonsai-like appearance. After several years, it may outgrow its indoor location and may need “pruning,” although it possesses amazing regenerative properties. Repotting can be a bit challenging due to its spines. Wrapping several layers of newspaper around the trunk where handling is required can be the best approach. Caution must be exercised when handling this plant, as it has spines.

Propagation:

Propagation of Pachypodium horombense can be achieved through seeds or, less commonly, cuttings. Fresh seeds offer an impressive success rate, with around 90% of them yielding new plants. For best results, soak the seeds in warm water for 24 hours before sowing them in a 5 mm deep, sterile, moist sandy medium. The recommended mix includes 4 parts fine and 4 parts coarse river sand, 1 part sieved, well-rotted compost, 1 part perlite, and 1 part vermiculite. Keep the mixture consistently moist and maintain a temperature of 27–35°C to facilitate rapid germination. The seeds begin to sprout within 3-4 days, but germination can continue erratically for up to 6 months. Additionally, Pachypodium horombense can be propagated through the removal of branches from older plants if pruning is required. When taking cuttings, allow them to dry for 5 to 8 days before potting them up. However, it’s worth noting that cuttings often fail to root successfully. Seedlings of Pachypodium horombense grow relatively slowly compared to other Pachypodium species. Young plants initially have more conical spines and show early signs of healthy swelling, branching, and even flowering.

Curiosity:

The name “Pachypodium” is derived from two Greek words: “pachys” (παχύς), meaning “thick” or “dense,” and “podion” (ποδίον), meaning “little foot” or “base.” The term was given to this genus of plants because of the thick, swollen base or caudex that many species in the genus possess, which resembles a thick, sturdy foot or base. The caudex serves as a water storage organ, helping the plants survive in arid and dry conditions. The species name “horombense”, instead, comes from the Horombe plateau in Madagascar, which is the native region of this species.

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